Jeffery H. Richardson

Photodetachment of electrons from large molecular systems: Cyclopentadienide and methylcyclopentadienide ions. An upper limit to the electron affinities of C5H5· and CH3C5H4·

The relative cross sections for the gas phase photodetachment of electrons have been determined for cyclopentadienide ions in the wavelength region 270–670 nm (4.59−1.85 eV) and for methylcyclopentadienide ions in the wavelength region 270–730 nm (4.59−1.70 eV). An ion cyclotron resonance spectrometer was used to generate, trap, and detect the negative ions and a 1000 W xenon arc lamp with a grating monochromator was employed as the light source. Both ions exhibited a monotonically increasing cross section over the entire wavelength region; consequently, only upper limits to the electron affinities could be determined: E.A. (C5H5 ·) ≤ 1.84±0.03 eV and E.A. (CH3C5H4 ·) ≤ 1.67±0.04 eV.

Photodetachment of electrons from trifluoromethyl and trifluorosilyl ions; the electron affinities of CF3− and SiF3−

Abstract The relative cross sections for the gas-phase photodetachment of electrons have been determined for CF 3 − and SiF 3 − in the wavelength region 300-420 nm (4.13-2.995 eV). Thermochemical studies show the electron affinity of the trifluoromethyl radical to be ca. 2.01 eV. The large difference between the photodetachment threshold and adiabatic electron affinity is attributed to the different geometries of the ion and neutral.

Photodetachment of NO−2; experimental evidence for a new isomer

Abstract The relative cross section for the gas phase photodetachment of electrons has been determined for nitrite ions in the wavelength region 280–740 nm (4.43-1.68 eV). The vertical detachment energy for ONO − has been determined to be ≈ 2.8 eV. Evidence is presented for a new isomer of NO − 2 .

Photodetachment of electrons from large molecular systems: Benzyl anion. An upper limit to the electron affinity of C6H5CH2

The relative cross section for the gas phase photodetachment of electrons has been determined for the benzyl anion in the wavelength region 870–1330 nm (1.43–0.93 eV). An ion cyclotron resonance spectrometer was used to generate, trap, and detect the negative ions and a 1000 W xenon arc lamp with a grating monochromator was employed as the light source. An upper limit to the electron affinity of the benzyl radical was determined to be 0.88±0.06 eV (20.4±1.5 kcal/mole).

The complexity of catalysis: origins of enantio- and diastereocontrol in sulfur ylide mediated epoxidation reactions

The reaction of chiral sulfur ylides with aldehydes and ketones has emerged as a useful asymmetric process for the synthesis of epoxides. Processes employing either catalytic or stoichiometric amounts of sulfides have been developed. Although a large number of chiral sulfur ylides have been tested in the epoxidation process, only a few have delivered high diastereo- and enantio- selectivity. This review examines the factors that influence stereocontrol (steric hindrance of the sulfide, ylide conformation, ylide face selectivity, reversibility of betaine formation, solvent, and metal salts). This analysis leads to the conclusion that high reversibility in betaine formation leads to high diastereoselectivity but low enantioselectivity, and non-reversible betaine formation leads to low diastereoselectivity and high enantioselectivity (provided that other criteria are met). To achieve both high diastereoselectivity and high enantioselectivity simultaneously, requires non-reversible formation of the anti-betaine and reversible formation of the syn-betaine. Thus, factors that influence the degree of reversibility in betaine formation are critically important since with subtle changes in reaction conditions (solvent, temperature, metal ions) both high enantio- and diastereoselectivity can often be achieved.

Photodetachment of electrons from phenoxide ion

The relative cross section for the gas phase photodetachment of electrons has been determined for phenoxide ions in the wavelength region 300−530 nm (3.10−2.34 eV). An upper limit to the electron affinity of C6H5O⋅ has been determined to be 2.35±0.06 eV. Evidence is presented for the existence of an autodetaching state in C6H5O−.

Photodetachment of electrons from ethyl nitrene anion. An upper limit to the electron affinity of C2H5N

Abstract N-nitrosodiethylamine has been found to be a good source of nitrogen containing anions, including C 2 H 5 N − . Photodetachment of electrons from C 2 H 5 N − has been studied with ion cyclotron resonance techniques. A threshold at 1.87 ± 0.16 eV can be taken as an upper limit to the electron affinity of ethyl nitrene.